Type of Document Master's Thesis Author Burnside, Wesley Michael URN etd-04142010-162912 Title The Influence of Two Estrogens on the Sex and Ovarian Development of Eastern Oysters (Crassostrea virginica) Maintained in a Closed Recirculating System Degree Master of Science (M.S.) Department Renewable Natural Resources Advisory Committee
Advisor Name Title Tiersch, Terrence R. Committee Chair Lynn, John W. Committee Member Supan, John Eric Committee Member Keywords
- oyster physiology
- reproductive hormones
Date of Defense 2010-03-30 Availability unrestricted AbstractAs a multi-million dollar industry, production of the eastern oyster Crassostrea virginica is significant to the economy of the nationís coastal regions. The cost of commercial oyster aquaculture has higher inputs than the oyster fishery, but larger, better quality oysters can be produced for culture by the stable availability of triploid individuals.
The goal of this project was to determine if the use of an estrogen, estradiol-17β or estradiol-3-benzoate, at a consistent environmental temperature would increase the percentage of females in a population, as well as ovarian development of eastern oysters. Ultimately, this could be applied to triploids to increase the number of viable oocytes produced for use in tetraploid induction. Tetraploids are used in direct triploid production to produce 100% triploid offspring when crossed with diploids.
When estradiol-17β was administered to oysters obtained late in the spawning season (August), there was no significant change in sex distribution. The gonad-to-body ratios on day 10 were significantly greater than on day 14 (P < 0.0001) and the stages of ovarian development in oysters treated with 150 ng differed from the other treatments (P = 0.002); significant differences were also seen between days 10 and 14 in this treatment (150 ng; P = 0.004).
When estradiol-3-benzoate was administered to out-of-season oysters obtained in February prior to the spawning season, there was a significant difference in sex distribution from days 10 to 14 between the non-injected control (P = 0.030) and 37.5 ng treatment (P = 0.010). There was not enough gonadal tissue to calculate the gonad-to-body ratio, but there were no significant differences in the stages of ovarian development.
Overall, the decrease in ovarian size over time is indicative of exogenous factors negatively affecting gonadal development. By increased management of factors such as high nutrient availability and decreased stress during transport and hormone administration could improve the response to estrogen treatment. Due to the short half-life of estrogens in vivo, a sustained-release system could also increase the treatment efficacy. Under the present conditions, there was not a clear, predictable effect of either estrogen on increasing gonadal development, maturity, or sex.
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